New evidence suggests Earth's oxygen levels fell after the Great Oxidation Event

According to Emma Hammarlund these 2 billion years old fossils represent an early life form that experimented with evolving into some kind of multicellular lifeform, but did not succeed. Credit: Abder El Albani

(Phys.org) —A team of European researchers has published a paper in the journal Proceedings of the National Academy of Sciences, offering a possible explanation for the apparent drop in early Earth's oxygen levels following what has come to be known as The Great Oxidation Event. In their paper, the team suggests evidence found in ocean sediments indicates that a sudden addition of carbon into the atmosphere resulted in a relatively quick reduction in oxygen.

Scientists have found multiple sources that indicate that approximately 2.3 billion years ago, oxygen levels in the atmosphere (and oceans) increased dramatically—they've named it the Great Oxidation Event. Though scientists can't explain exactly why this happened, they do believe it occurred during a time of major glaciation, and was perhaps the result of the evolution of bacteria. Since that time, scientists have believed that changes in oxygen levels have been the result of a series of steps rather than great upheavals. Now, new research by the European team suggests that a change of thinking might be in store.

To try to better understand what went on with the atmosphere as the Earth was evolving from a lifeless planet to the rich biota filled environment of today, scientists look to rocks formed millions or even billions of years ago, and to ocean sediments. In this latest effort, the research group looked to such samples gathered from the ocean floor off the coast of western Africa's Republic of Gabon. Because sediments collect so slowly over time, analyzing them offers a glimpse into the past, similar in many respects to ice samples taken from polar climates.

The samples they retrieved offered evidence of ocean (and therefore atmospheric) oxygen levels, before, during and after the Great Oxidation Event, and surprisingly, indicated that shortly after the large infusion of oxygen, there was a fall. The researchers attribute this fall to an increase in carbon and iron in the atmosphere, part of what they call the largest positive carbon-isotope excursion in the history of the planet. The oxygen reacted, they say, with iron and carbon forming oxides that were carried to the ocean floor. Though the carbon excursion can't be explained either, it is believed it was likely tied to the evolution of life in the oceans.

More information:
Oxygen dynamics in the aftermath of the Great Oxidation of Earth's atmosphere, Published online before print September 30, 2013, DOI: 10.1073/pnas.1315570110

Abstract
The oxygen content of Earth's atmosphere has varied greatly through time, progressing from exceptionally low levels before about 2.3 billion years ago, to much higher levels afterward. In the absence of better information, we usually view the progress in Earth's oxygenation as a series of steps followed by periods of relative stasis. In contrast to this view, and as reported here, a dynamic evolution of Earth's oxygenation is recorded in ancient sediments from the Republic of Gabon from between about 2,150 and 2,080 million years ago. The oldest sediments in this sequence were deposited in well-oxygenated deep waters whereas the youngest were deposited in euxinic waters, which were globally extensive. These fluctuations in oxygenation were likely driven by the comings and goings of the Lomagundi carbon isotope excursion, the longest–lived positive ?13C excursion in Earth history, generating a huge oxygen source to the atmosphere. As the Lomagundi event waned, the oxygen source became a net oxygen sink as Lomagundi organic matter became oxidized, driving oxygen to low levels; this state may have persisted for 200 million years.

Related Stories

Oxygen appeared in the atmosphere up to 700 million years earlier than we previously thought, according to research published today in the journal Nature, raising new questions about the evolution of early life.

Most researchers imagine the initial oxygenation of the ocean and atmosphere to have been something like a staircase, but with steps only going up. The first step, so the story goes, occurred around 2.4 billion years ago, ...

(PhysOrg.com) -- Geologists may have uncovered the answer to an age-old question - an ice-age-old question, that is. It appears that Earth's earliest ice ages may have been due to the rise of oxygen in Earth's atmosphere, ...

An international team of scientists, including geochemists from the University of California, Riverside, has uncovered new evidence linking extreme climate change, oxygen rise, and early animal evolution.

(Phys.org)—There is evidence that some microbial life had migrated from the Earth's oceans to land by 2.75 billion years ago, though many scientists believe such land-based life was limited because the ozone layer that ...

The appearance of oxygen in the Earth's atmosphere probably did not occur as a single event, but as a long series of starts and stops, according to an international team of researchers who investigated rock cores from the ...

Recommended for you

The East Antarctic Ice Sheet locks away enough water to raise sea level an estimated 53 meters (174 feet), more than any other ice sheet on the planet. It's also thought to be among the most stable, not gaining or losing ...

Volcanic eruptions are the most spectacular expression of the processes acting in the interior of any active planet. Effusive eruptions consist of a gentle and steady flow of lava on the surface, while explosive eruptions ...

From North Dakota to Ohio to Pennsylvania, hydraulic fracturing, also known as fracking, has transformed small towns into energy powerhouses. While some see the new energy boom as benefiting the local economy and decreasing ...

Environmental scientists from The Open University (OU) have discovered that trees growing in the Amazon floodplains surrounding the Amazon River emit as much methane (CH4) into the atmosphere as all of the world's oceans. ...

It may take until the 2060s to know how much the sea level will rise by the end of this century, according to a new Rutgers University-New Brunswick-led analysis. The study is the first to link global and local sea-level ...

3 comments

The answer will require addressing a single simple question: "Where was the carbon *before* it became oxidized to CO2, HCO3-, and CO3= in water and rocks?" Was it as elemental carbon, methane, or something else?

The observation is in itself an answer to the question "what oxygen levels were present after the GOE?"

""Where was the carbon *before*".

There isn't any model of carbon sourcing specifically involved, the isotope excursion depends on istope fractional sorting which happens in many geological and biological processes when carbon is recycled through the geosphere.

The biosphere carbon has mostly been scavenged from the original CO2 atmosphere, there were never any carbon shortage. "Carbonate rocks are rare, indicating that the oceans were more acidic due to dissolved carbon dioxide than during the Proterozoic.[7]" [ http://en.wikiped.../Archean ]

Life evolved chemically as a catalyst of redox reactions, in the electron sink end as a way to rust Fe faster (reduced Fe supplied by heating crust under plate tectonics) and in the source end originally as a way to convert the atmospheric CO2 to CH4 faster (making hydrocarbons).

[cont] Why it evolved that way is due to free forcing of redox reactions, meaning they want to increase entropy flow to the universe vacuum by the fastest reaction channel they can evolve.

And why there were such redox reactions is due to geochemistry. We now know that we are an evolved branch of geochemistry because we clade with alkaline hydrothermal vent redox chemistry (Lane & Martin). Ultimately the driving force was the (now cooling) heated core of Earth, today supplemented by the free energy from solar radiation.

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.